1. Field of the Invention
The present invention relates to an in-plane switching mode liquid crystal display (LCD) device. More particularly, the present invention relates to an in-plane switching mode liquid crystal display device in which a pixel is divided into at least three domains to improve the viewing angle and compensate a color shift problem of the device.
2. Description of the Related Art
Since the introduction of portable electronic devices such as mobile phones, PDAs, and notebook computers, flat panel display devices such as a Plasma Display Panel (PDP), Field Emission Display (FED), Vacuum Fluorescent Display (VFD), and liquid crystal display (LCD) devices have been actively developed. Among the flat panel display devices, the liquid crystal display device is primarily used because of mass production, high definition and effective driving method.
The liquid crystal display device can be divided into various display modes according to the alignment of liquid crystal molecules. The TN (twisted nematic) mode liquid crystal display device is mainly used because of its effective black mode, fast response time and low driving voltage. In the TN mode liquid crystal display device, the liquid crystal molecules are aligned perpendicular to the substrate when an electric field is applied. Accordingly, there is a problem of a narrow viewing angle when the driving voltage is applied.
In order to overcome this problem, liquid crystal display devices having a wide viewing angle characteristics, such as an in-plane switching (IPS) mode liquid crystal display device, have been introduced. In the IPS mode liquid crystal display device, the electric field applied to the liquid crystal molecules is parallel to the surface of the substrate. Thus, the liquid crystal molecules are aligned parallel to the surface of the substrate which results in an improved viewing angle.
FIG. 1 illustrates an IPS mode liquid crystal display device.
As shown in the related art IPS mode liquid crystal display device in FIG. 1, the alignment direction is formed in a predetermined angle to an elongated direction of the gate line to align liquid crystal molecules 32 of the liquid crystal layer 30. As shown in FIGS. 1A and 1B, when an electric field is not applied (the field-off state), the liquid crystal molecules are aligned along the alignment direction.
In this IPS mode liquid crystal display device, however, there is problem that the color is shifted along the viewing angles. As shown in FIG. 1C, the liquid crystal molecules near the first substrate 10 are aligned parallel to the elongate direction of the gate line by the electric field and the liquid crystal molecules near the second substrate 20 are aligned in the angle of 90° to 180° with respect to the gate line, so that the liquid crystal molecules are twisted from the first substrate 10 to the second substrate 20. Thus, in the viewing angle directions X and Y, the color is shifted to blue and yellow along the viewing direction. As a result, the image quality is deteriorated. In order to overcome this problem, an IPS mode liquid crystal display device has been introduced as shown in FIG. 2 and disclosed in Korea Patent Application No. 1996-23115. In this IPS mode liquid crystal display device, a pixel, defined by the gate line 1 and data line 3, is divided into two domains. That is, the pixel is divided into two domains I,II by a common line 6 and a pixel electrode line 8 that are respectively connected to the common electrode 5 and the pixel electrode 7.
In the pixel, the thin film transistor 15 including a gate electrode 16, a semiconductor layer 17, a source electrode 18 and a drain electrode 19 is disposed at the crossing of the gate line 1 and the data line 3. The signal from an outer driver is supplied to the pixel electrode 7 through the thin film transistor, and thus an electric field parallel to the surface of the substrate is applied in the liquid crystal layer.
The alignment direction (i.e., a rubbing direction) is formed in the elongated direction of the data line 3. Further, the elongated direction of the common electrode 5 and the pixel electrode 7 in the first domain I is different from that of the common electrode 5 and the pixel electrode 7 in the second domain II. Specifically, the common electrode 5 and the pixel electrode 7 are arranged in a slanted direction with reference to the gate line 1, and the common electrodes 5 and the pixel electrodes 7 disposed respectively in the first domain I and the second domain II are symmetric and centered on the common line 6. Accordingly, the color shifts in the first domain I and the second domain II compensate each other to prevent color shift in the pixel.
In this IPS mode liquid crystal display device having two domains, however, improvement of the viewing angle characteristic may be limited. When comparing the IPS mode liquid crystal display device having two domains with a cathode ray tube, for example, there are problems that the viewing angle characteristic is low and the color is shifted.